This invention relates to the hydrogenation of carboxylic acids to form alcohols. More specifically the invention relates to the vapor phase catalytic hydrogenation of carboxylic acids.
Carboxylic acids may be obtained from the carboxylation of olefins. The hydrogenation of carboxylic acids and their derivatives to obtain alcohols has previously been described in the art. The product alcohols are useful as solvents, chemical intermediates, and fuel. U.S. Pat. No. 2,093,159 discloses the catalytic hydrogenation of esters of carboxylic acids over catalytic substances such as copper, nickel, silver, zinc, cadmium, lead or cobalt and activating substances such as various transition metals, alkali metals, alkaline earth metals or rare earth metals.
U.S. Pat. No. 2,110,483 discloses a process for the manufacture of higher molecular weight alcohols from aliphatic carboxylic acids and their derivatives by hydrogenation under pressures of between 50 and 400 atmospheres and in the presence of catalysts which include copper, chromium, nickel, uranium, cobalt, zinc, cadmium, molybdenum, tungsten and vanadium.
U.S. Pat. No. 2,275,152 discloses the catalytic hydrogenation of carboxylic acid anhydrides over a mixture of chromites or chromates of hydrogenating metals selected from silver, cadmium, copper, lead, mercury, tin, bismuth, iron, cobalt, nickel, magnesium, zinc and manganese.
U.S. Pat. No. 2,322,098 and its related patents disclose the catalytic hydrogenation of alicyclic carboxylic acids in the presence of catalysts similar to those set forth in U.S. Pat. No. 2,093,159.
U.S. Pat. No. 2,607,807 discloses the preparation of alcohols from carboxylic acids in the liquid phase in the presence of a catalyst containing ruthenium and optionally sodium, potassium, barium, silver, calcium, strontium and magnesium.
U.S. Pat. No. 4,104,478 discloses the hydrogenation of fatty acids in the presence of activated rhenium metal in combination with an extrinsic metal catalyst in the form of one of the platinum metals.
U.S. Pat. No. 4,113,662 discloses the hydrogenation of esters to alcohols in the presence of a catalyst comprising cobalt, zinc and copper at a pressure of 500--10,000 psig, preferably in the liquid phase.
We have found that the hydrogenation of carboxylic acids may be conducted in the vapor phase at moderate temperatures and pressures to provide good yields of the corresponding alcohols in the presence of an excess of water vapor over promoted ruthenium catalysts. We have further found that contacting the carboxylic acids in the presence of these catalysts at reaction temperature and pressures in the absence of an excess of water vapor results in the production of an ester of the carboxylic acid, wherein both the carboxylic acid and the ester functionality correspond to the reactant carboxylic acids.